There was the scene that Rainer and Bertholdt took Eren up on the hill during training when Eren couldn't stay up on the 3D testing. That was already suspicious as all hell including their physical resemblances to the Armor and Colossus titans. The one I'm not sure who it would be is the Beast titan, actually aside from the Annie faction and the wall smashing faction, I'm pretty sure we'll find out most of the other titans are as unique as anyone else in their thoughts. Annie probably wanted Eren to make an ally. She seemed to have an appreciation for him ever since he learned her takedown move back in training.

I'm also suspecting that Crista doesn't know jack. Ymir maybe. But Crista may be some other kind of key, maybe someone unconsciously part of the plan, and if it's the wall priests probably has something to do with being able to make or repair the walls.

Last thought before I shut up was to the point about Beast having ability to create and control Titans. It was already hinted at back with Annie at the forest trap that she could call Titans and cause them to enter some kind of mode where they become Abnormals. Which makes it not at all out of the question that any of the titans could actually speak (Eren is a sort of berserker Titan so I wouldn't expect him to) and lead. How deep that ability goes to be able to control them like Beast did is probably more to the individual, maybe even to the point of being able to have your own sort of titan brood that obey like children.